A Korean-Canadian pastor arrested in North Korea has confessed to "subversive plots" against the communist nation during a news conference Thursday, Pyongyang's official news agency said.

The Rev. Lim Hyeon-soo (Rim Hyon-su), 60, of Light Korean Presbyterian Church near Toronto was detained after entering the North via China on a humanitarian mission in late January.

Pyongyang's Korean Central News Agency accused him of acting as "a servant of the U.S. imperialists and South Korean puppet group."

"He malignantly hurt the dignity of the supreme leadership and social system of the DPRK and resorted to subversive plots and activities in a sinister bid to build a religious state in the DPRK while frequenting it under the guise of 'humanitarian aid' and 'free donation' over the past 18 years," KCNA said.

"He confessed to all his crimes in the course of the investigation by the competent organ," it said.

KCNA quoted the pastor as saying that he delivered a "report on what is going on in North Korea before tens of thousands of South Koreans and overseas Koreans at a sermon on Sundays at my church and during preaching tours of more than 20 countries including Canada, the U.S., south Korea, Japan and Brazil."

"Each time I malignantly slandered the dignity and social system of the DPRK," he was quoted as saying.

The pastor also confessed that he met with the U.S. ambassador to Mongolia in 1996 and discussed the issue of helping more than 500 North Korean defectors go to South Korea via Mongolia every year, according to KCNA.

He also told the news conference that he received a GPS device from a Korean American named Dennis Kim and handed it to a Korean Chinese broker helping North Koreans defect from their communist homeland, KCNA said.

The Unification Ministry said that it is "improper" for North Korea to detain the pastor for charges of what the North calls "subversive plots."

"In terms of four South Korean nationals detained in the North, it is not easy to figure out their whereabouts," Jeong Joon-hee, the ministry spokesman, said in a regular press briefing on Friday.

"The government is making efforts via diplomatic channel."

Seoul has called on Pyongyang to set free the four South Koreans detained in North Korea including a New York University student and missionary Kim Jung-wook.

Christian missionaries have often been detained in the North.

Kenneth Bae, one such missionary, was released in November after about two years of detention in the communist nation. Bae, who entered the North in late 2012, was sentenced to 15 years of hard labor for unspecified anti-state crimes. (Yonhap)